Moose, the feisty Jack Russell terrier who played Eddie for 10 years on TV's Frasier, has died, his trainer Mathilde Halberg tells PEOPLE.

"He was 16-and-a-half years old, and he just had an incredible charisma and was a such a free spirit," said Halberg. Moose, considered the Lassie of the '90s, died Thursday night of old age at Halberg's Los Angeles-area home.

Moose retired from showbiz when he was 10, and, although he also played a starring role in the 2000 Frankie Muniz-Kevin Bacon feature My Dog Skip (as the older Skip), he was best known for stealing scenes from Kelsey Grammer on the long-running Emmy-winning NBC sitcom.

"He was always trying to put Frasier in uncomfortable circumstances," said his trainer, who had rescued him in the early 1990s.

"I saved him from the pound. His owners called me as a last resort," Halberg recalled. "He was extremely mischievous, always escaping, chewing up things and running off. When he killed a neighbor's cat and chased some horses, that was it."

Not that anyone who owns a Jack Russell would find such behavior surprising. "But then," remembered his trainer, "he began his career, and he will never be forgotten."